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Utilization of Incinerator Bottom ASH - Legal, Environmental and Engineering Aspects
Wasre Marenair in f orrctrucimt J . J J . X . Gounrons. H A van der Slooi und Th.G. Aaihers (Edrrorr) ' C ) 1991 EIsewc, Scre,rce hrhlrrhrr, H I,A i l r r g h r reserved.
UTILIZATION OF INCINERATOR BOTTOM ASH LEGAL, ENVIRONMENTALAND ENGINEERING ASPECTS
207
-
J. Hartlkn' and T. Lundgren2
' Swedish Geotechnical Institute, S-581 01 Linkliping (Sweden) * Terratema AB, FOA-huset, S-583 30 Linkliping (Sweden) SUMMARY
The legal, environmental and engineering aspects of utilizing incinerator bottom ash have been studied in a comprehensive project. The study shows that several laws may be applicable in Sweden when utilizing a residue. Present legislation is not geared to the new situation where such utilization is concerned. Based on measured chemical and physical properties, a list of important parameters is presented and discussed in the paper. Impact on the environment is evaluated and related to other sources of environmental impact and the vulnerability of the environment. The conclusion is that graded bottom ash can be utilized, but with some limitations. Finally, the paper discusses how to regulate the use of incinerator bottom ash.
1.
BACKGROUND
For several years now, waste management in Sweden has been aimed at increased reclamation and recycling. It is only natural that the ambition of plant owners is to recycle the residual pmducts of incineration as well. In regard to the use of such products as high-grade fill and roadbuilding materials, other reasons also speak in favour of such usage, chief among them being the increasingly shortage of natural materials like gravel, sand and crushed rock, as well as the need to spare these natural resources for reasons of nature conservation or as ground water reservoirs. The consumption of natural materials in Sweden for roads and fill is at present about 90 million tonnes per year, mainly obtained from about 7,000 sources scattered all over the country. The potential for producing graded slag at the country's existing waste treatment piants corresponds to about 0.3 million tonnes per year. Concurrently, about 200,000 m3 of landfill space would be saved annually.
208
Two fundamental conditions for utilizing slag are that the technical results of its use are satisfactory and that its effect on the environment can be accepted. It must be possible to describe and quantify its effect on the environment in absolute terms and in relation to the alternatives. From an environmental viewpoint, it is primarily the leaching of metals which must be taken into consideration. The leaching of salts may also have important local consequences. The problems of carrying out such an assessment arise from the fact that leaching is difficult to quantify and that general reference values are either unavailable, of doubtful accuracy or unrepresentative of the cases in question. A major project has been carried out from 1987 to 1991 in order to determine the physical and chemical properties of incinerator bottom ash and coal bottom ash from grate firing and, on the basis of the results obtained, to define rules for facilitating official approval of re-use (Lundgren & Hartltn, 1991). The project included field and laboratory tests, as well as an evaluation of the environmental impact and current legal restrictions and/or prospects.
2.
ENVIRONMENTAL LEGISLATION
The use of residual products such as slag and bottom ash from the combustion of different solid fuels for the construction of roads, for example, must be taken into consideration from the viewpoint of environmental protection. This means that the Environment Protection Act (ML) is applicable. In Sweden, however, it is not the utilization of the residual product in itself that requires a licence, but the use of "real property" in a specified manner when residual products constitute an element. This also applies to the controlled tipping of the residual product, described as "deposition of solid waste" in the Environment Protection Act and judged in accordance with this Act. Uncertainty has existed in regard to whether or not a licence is obligatory under the Environment Protection Act for the utilization of slag and bottom ash. This has given rise to the need for a set of rules defining which products may be used, as well as where and how they may be used. With reference to such a set of rules, general licences can be granted in certain regions or for certain incineration plants.
3.
ASH PROPERTIES
One requirement on the utilization of bottom ash will be that the ash is graded by using screens as well as drum magnets. After grading, about 70% can be regarded as a suitable substitute for coarse aggregate. About one-third of the remaining 30% from the grading operation consists of coarse scrap that can be sold and the other two-thirds will usually have to be disposed of in some way. The constituents of the graded bottom ash have been identified (Jacobsson, 1989) and are shown in Table 1. The content is shown for different grain size intervals.
209
TABLE 1 Main constituents of graded bottom ash used in Malmij (Jacobsson, 1989).
FRESH ASH FRACTION 5.6-8
mm Magnetic Non-magnetic slag Glass Ceramic mtrl Stone Paper
45.0 44.9 1.3 8.7 0.1
AGED ASH FRACTION
8-11.2 11.2-16 mm mm WEIGHT
5.6-8
8-11.2
11.2-16
mm
mm
mm
55.6 40.0 2.4 2.0
43.4 49.0 2.3 5.3
50.6 35.9 3.4 10.1
WEIGHT
37.9 49.7 3.9 8.5
28.5 56.6 5.0
9.9
As can be. seen from the table, about 40% is viueous material. It should also be noted that magnetic separation is extremely efficient as no magnetic materials at all were detected. “Aged ash” is ash which has been kept in storage for a period of time before utilization. Experience in Europe is that such storage results in a more stable product (HartlCn, 1988). It is believed that oxidation of iron and other reactions take place during storage (Aubrey et al, 1986). Experience in Germany is that temporary storage prevents future swelling of the ash. The water content of fresh ash (about one or two months old) before Iaying was about 23% and of aged ash about 16%.Water content varies widely, however. The lower water content of aged ash makes it easier to compact. Using a heavy vibrating roller (about 10 tomes), a degree of compaction better than 90% modified Proctor was achieved (HartlCn & Rogbeck, 1989). Graded bottom ash has been used on a trial basis in test roads. The results are so far promising and indicate that the properties when bottom ash is used are approximately the same as when natural aggregates are used. Leaching properties have been studied in the laboratory by means of sequential batch leaching and diffusion leaching tests.
4.
ENVIRONMENTAL IMPACT
The leaching process in a fill of bottom ash above ground water level is highly complex. Since the porous material is unsaturated by water and almost completely dry during certain periods, the concentrations of the dissolved substances will not be constant in time and the rate of diffusion in the material will therefore vary (in time and space). The leaching process cannot therefore be simulated in a natural manner in the laboratory and particularly not in accelerated experiments.
210 Conventional shaking tests and special diffusion tests both indicate that the leachate content will decrease comparatively rapidly. There is not a lot of difference in this respect between the salts (sulphate and chloride) and metals in general. Some metals differ from the general pattern. however. Leaching tests cannot be verified until more leachate has been examined from the test roads and in particular from the road structure under the asphalt pavement (Kullberg, 1990). A general assessment of the effect that graded bottom ash fill may conceivably have on the nearest
(most sensitive) watercourse can be made if a number of assumptions are taken:
*
The formation of leachate corresponds to the percolation through permeable fractured asphalt (100 mm/year).
*
A sorption of transported elements corresponding to 50% takes place in the underlying soil.
*
The leachate is diluted only with such surface water and ground water as have formed in its "own" runoff area.
*
No sorption in the surface watercourse of the substances in question from the bottom ash is expected.
Dilution of the leachate in the internal runoff area, that is in the layers of soil and eventually in the local surface watercourse, will naturally depend on the size of the runoff area or its distance from the fill. In most cases, however, dilution corresponding to a factor of at least 100 within reasonable distance of a sizeable fill is likely to be achieved. If the background level is the same as that in unaffected watercourses, then increased contents and corresponding contamination factors cdculated according to the National Environment Protection Boards "General Advice", Table 2, will then be obtained in the watercourse.
21 1
TABLE 2 The "normal" chemical composition of the leachatefrom graded slag is assessed on the basis of the project results as well as on the corresponding "unaffectedbackground content in surface waters and the calculated content resulting from the discharge of leachate into local watercourses. ~
Substance/ parameter
Content in leachate from graded slag
Content background surface water
Content local watercourse
Contamination factor
Chloride (mg/l) Sulphate ( m a )
120 300
4 15
5.1 17.8
1.3 1.2
30 0.02 0.3
1 .Ol 1.2 1.1 1.3
0.74
1.5 1.5 1.5
Aluminium (p@) Cadmium (pg) Chromium (p@) copper (pg/l)
50 0.5 4 20
0.7
30.2 0.025 0.34 0.89
25 10 100
0.5 0.2 2.0
0.30 3.0
In spite of the conservative assumptions in the calculations, the contamination factor for nickel, lead and zinc would obviously reach the limit between "insignificant effect" (up to 50% increase) and "significant effect" (50-200% increase). However, it should be noted that this applies to an initial stage before dilution of the leachable part of the residual products starts to occur. A reduction of the leachate content by a factor of 5-10 is obtained after only a few years. The environmental impact should not be evaluated solely on the basis of concentrations in leachate and thus in the affected ground water and/or surface water. The total amount in grammes, for example, is also of importance. Some data and comparisons are given in Table 3.
212
TABLE 3
Calculated quantities leachedfrom a I km stretch of road constructed of different materials, expressed in grammeslyear. The calculation is in respect of the initial stage of the leaching process (year 1). Metal Al Leachate from
Cd
Cr
cu
Ni
Pb
Zn
Graded slag (Malmo)
16-250
0.2-1.2
3-9
13-100
20-80
0.6-27
10-800
Graded slag (Linkoping)
7
<0.2
3
6
2
0.7
14
Natural gravel (Malmo)
800-3700 0.3-4
2-14
6-460
5-30
1-360
10-900
Natural gravel (LinkBping)
8
<0.2
2
14
0.1
0.1
19
Run-off water from test road (Malmo)
1-320
1-3
3-12
38-165
5-120
1-29
13-220
In all probability, the leaching properties of most fill materials in urban environments axe generally not more favourable than those of graded slag. In order to correspond to the background level in a natural environment (ground water), the leachate from such "graded slag" as has been studied here requires little dilution - in the order of a factor of 10. On the other hand, the amount of undiluted leachate necessary to achieve a significant effect on the environment corresponds to a factor 3-20 times higher than has been obtained in the leachate from "graded slag" and incinerator bottom ash. Calculation of leaching from natural gravel in Malmo (Table 3) is based, like the other annual amounts, on the data obtained for the test road in Malmo. It should be pointed out that this data only represents a short period of leaching and may be influenced by such factors as the infiltration of surface water and dust from various activities in the m a . In spite of the pronounced difference in leaching between natural gravel in Malmo and natural gravel in Linkoping, leaching must still be regarded as slight in all cases.
213
5.
PROCEDURES FOR UTILIZATION
The study and subsequent discussions with the Swedish EPA have shown that the utilization of screened bottom ash does not have a critical impact on the environment. The materiak should have the following properties: -
Rescreened ash through the separation of magnetic materials
- Maximum grain size 50 mm - No more than 10% of the particles smaller than 0.06 mm
-
The content of metals in leachates from the laboratory must not exceed those in the leachates
studied in the project - Loss on incineration less than 4% - The ash must be kept in storage for at least 3 months. The slag can be used chiefly for the following applications:
-
Embankment fill for roads Reinforcement material for low-traffic roads and bicycle paths - Fill under light buildings and floor structures
For the present, the guidelines below should normally be followed:
- The thickness of the fill should be limited to 3.0 m - The bottom ash should be placed primarily above the ground water - The bottom ash should be used primarily in urban areas and as fill.
level and below pavement
In an initial stage, general advice will be prepared for a small number of products, including sorted bottom ash from incineration and cementstabilized coal fly ash, for example. When sufficient experience has been gained over a few years, a general system ought to be drawn up and made available. The responsibility for this rests with the National Environment Protection AgeriCY.
The various suppliers ought to draw up procedures for the delivery of ash which include the following particulars: - quantity delivered - environmental quality assurance in respect of the delivered ash -
-
location
plan and section - control programme, if necessary
214
6.
ACKNOWLEDGEMENT
The authors wish to thank Sysav AB, who has given permission to publish data from the on-going project. We aslo want to thank Stiftelsen Reforsk, who is financing a major part of the studies.
7.
REFERENCES
Aubry, P,, Poncelet, E. & Billard, H. (1986).Mkheferes des usines d’aincineration d’ordures mtnageries: Charactdristiqueet utilisations - A.N.R.E.D. Service Recherches, Etudes et Dtvelopment. Hartlh, J. (1988). Incinerator ash utilkization in some countries in Europe. Roc. Ash IConference. Philadelphia. Hartlh, J. & Rogbeck, J. (1989). Sorted incinerator slag used as fill material. Roc. Int. Conf. on Municipal Waste Combustion, Vol. 1, p. 5B:1-13. ISBN 0-662 16891-7.
Jacobson, T. (1989). Provvag med sopfiirbrhningsrest i forsttirkningslager.Sysav, Malmii. National Road and Traffic Institute. VTI Notat V 104. Linkoping. Kullberg, S. (1990). Miljiiteknisk utvtirdering av provvagar vid an viindning av sopslagg och kolbottenaska i Malmo och LinkUping 1988-1990. Swedish Geotechnical Institute, Report No 2-482188. Lidcoping. Lundgren, T.& Hartlh, J. (1991). Slagganvandning - Teknik och miljo. Slutrapport. Stiftelsen Reforsk. Report (In print). Malmo.
UTILIZATION OF INCINERATOR BOTTOM ASH LEGAL, ENVIRONMENTALAND ENGINEERING ASPECTS
207
-
J. Hartlkn' and T. Lundgren2
' Swedish Geotechnical Institute, S-581 01 Linkliping (Sweden) * Terratema AB, FOA-huset, S-583 30 Linkliping (Sweden) SUMMARY
The legal, environmental and engineering aspects of utilizing incinerator bottom ash have been studied in a comprehensive project. The study shows that several laws may be applicable in Sweden when utilizing a residue. Present legislation is not geared to the new situation where such utilization is concerned. Based on measured chemical and physical properties, a list of important parameters is presented and discussed in the paper. Impact on the environment is evaluated and related to other sources of environmental impact and the vulnerability of the environment. The conclusion is that graded bottom ash can be utilized, but with some limitations. Finally, the paper discusses how to regulate the use of incinerator bottom ash.
1.
BACKGROUND
For several years now, waste management in Sweden has been aimed at increased reclamation and recycling. It is only natural that the ambition of plant owners is to recycle the residual pmducts of incineration as well. In regard to the use of such products as high-grade fill and roadbuilding materials, other reasons also speak in favour of such usage, chief among them being the increasingly shortage of natural materials like gravel, sand and crushed rock, as well as the need to spare these natural resources for reasons of nature conservation or as ground water reservoirs. The consumption of natural materials in Sweden for roads and fill is at present about 90 million tonnes per year, mainly obtained from about 7,000 sources scattered all over the country. The potential for producing graded slag at the country's existing waste treatment piants corresponds to about 0.3 million tonnes per year. Concurrently, about 200,000 m3 of landfill space would be saved annually.
208
Two fundamental conditions for utilizing slag are that the technical results of its use are satisfactory and that its effect on the environment can be accepted. It must be possible to describe and quantify its effect on the environment in absolute terms and in relation to the alternatives. From an environmental viewpoint, it is primarily the leaching of metals which must be taken into consideration. The leaching of salts may also have important local consequences. The problems of carrying out such an assessment arise from the fact that leaching is difficult to quantify and that general reference values are either unavailable, of doubtful accuracy or unrepresentative of the cases in question. A major project has been carried out from 1987 to 1991 in order to determine the physical and chemical properties of incinerator bottom ash and coal bottom ash from grate firing and, on the basis of the results obtained, to define rules for facilitating official approval of re-use (Lundgren & Hartltn, 1991). The project included field and laboratory tests, as well as an evaluation of the environmental impact and current legal restrictions and/or prospects.
2.
ENVIRONMENTAL LEGISLATION
The use of residual products such as slag and bottom ash from the combustion of different solid fuels for the construction of roads, for example, must be taken into consideration from the viewpoint of environmental protection. This means that the Environment Protection Act (ML) is applicable. In Sweden, however, it is not the utilization of the residual product in itself that requires a licence, but the use of "real property" in a specified manner when residual products constitute an element. This also applies to the controlled tipping of the residual product, described as "deposition of solid waste" in the Environment Protection Act and judged in accordance with this Act. Uncertainty has existed in regard to whether or not a licence is obligatory under the Environment Protection Act for the utilization of slag and bottom ash. This has given rise to the need for a set of rules defining which products may be used, as well as where and how they may be used. With reference to such a set of rules, general licences can be granted in certain regions or for certain incineration plants.
3.
ASH PROPERTIES
One requirement on the utilization of bottom ash will be that the ash is graded by using screens as well as drum magnets. After grading, about 70% can be regarded as a suitable substitute for coarse aggregate. About one-third of the remaining 30% from the grading operation consists of coarse scrap that can be sold and the other two-thirds will usually have to be disposed of in some way. The constituents of the graded bottom ash have been identified (Jacobsson, 1989) and are shown in Table 1. The content is shown for different grain size intervals.
209
TABLE 1 Main constituents of graded bottom ash used in Malmij (Jacobsson, 1989).
FRESH ASH FRACTION 5.6-8
mm Magnetic Non-magnetic slag Glass Ceramic mtrl Stone Paper
45.0 44.9 1.3 8.7 0.1
AGED ASH FRACTION
8-11.2 11.2-16 mm mm WEIGHT
5.6-8
8-11.2
11.2-16
mm
mm
mm
55.6 40.0 2.4 2.0
43.4 49.0 2.3 5.3
50.6 35.9 3.4 10.1
WEIGHT
37.9 49.7 3.9 8.5
28.5 56.6 5.0
9.9
As can be. seen from the table, about 40% is viueous material. It should also be noted that magnetic separation is extremely efficient as no magnetic materials at all were detected. “Aged ash” is ash which has been kept in storage for a period of time before utilization. Experience in Europe is that such storage results in a more stable product (HartlCn, 1988). It is believed that oxidation of iron and other reactions take place during storage (Aubrey et al, 1986). Experience in Germany is that temporary storage prevents future swelling of the ash. The water content of fresh ash (about one or two months old) before Iaying was about 23% and of aged ash about 16%.Water content varies widely, however. The lower water content of aged ash makes it easier to compact. Using a heavy vibrating roller (about 10 tomes), a degree of compaction better than 90% modified Proctor was achieved (HartlCn & Rogbeck, 1989). Graded bottom ash has been used on a trial basis in test roads. The results are so far promising and indicate that the properties when bottom ash is used are approximately the same as when natural aggregates are used. Leaching properties have been studied in the laboratory by means of sequential batch leaching and diffusion leaching tests.
4.
ENVIRONMENTAL IMPACT
The leaching process in a fill of bottom ash above ground water level is highly complex. Since the porous material is unsaturated by water and almost completely dry during certain periods, the concentrations of the dissolved substances will not be constant in time and the rate of diffusion in the material will therefore vary (in time and space). The leaching process cannot therefore be simulated in a natural manner in the laboratory and particularly not in accelerated experiments.
210 Conventional shaking tests and special diffusion tests both indicate that the leachate content will decrease comparatively rapidly. There is not a lot of difference in this respect between the salts (sulphate and chloride) and metals in general. Some metals differ from the general pattern. however. Leaching tests cannot be verified until more leachate has been examined from the test roads and in particular from the road structure under the asphalt pavement (Kullberg, 1990). A general assessment of the effect that graded bottom ash fill may conceivably have on the nearest
(most sensitive) watercourse can be made if a number of assumptions are taken:
*
The formation of leachate corresponds to the percolation through permeable fractured asphalt (100 mm/year).
*
A sorption of transported elements corresponding to 50% takes place in the underlying soil.
*
The leachate is diluted only with such surface water and ground water as have formed in its "own" runoff area.
*
No sorption in the surface watercourse of the substances in question from the bottom ash is expected.
Dilution of the leachate in the internal runoff area, that is in the layers of soil and eventually in the local surface watercourse, will naturally depend on the size of the runoff area or its distance from the fill. In most cases, however, dilution corresponding to a factor of at least 100 within reasonable distance of a sizeable fill is likely to be achieved. If the background level is the same as that in unaffected watercourses, then increased contents and corresponding contamination factors cdculated according to the National Environment Protection Boards "General Advice", Table 2, will then be obtained in the watercourse.
21 1
TABLE 2 The "normal" chemical composition of the leachatefrom graded slag is assessed on the basis of the project results as well as on the corresponding "unaffectedbackground content in surface waters and the calculated content resulting from the discharge of leachate into local watercourses. ~
Substance/ parameter
Content in leachate from graded slag
Content background surface water
Content local watercourse
Contamination factor
Chloride (mg/l) Sulphate ( m a )
120 300
4 15
5.1 17.8
1.3 1.2
30 0.02 0.3
1 .Ol 1.2 1.1 1.3
0.74
1.5 1.5 1.5
Aluminium (p@) Cadmium (pg) Chromium (p@) copper (pg/l)
50 0.5 4 20
0.7
30.2 0.025 0.34 0.89
25 10 100
0.5 0.2 2.0
0.30 3.0
In spite of the conservative assumptions in the calculations, the contamination factor for nickel, lead and zinc would obviously reach the limit between "insignificant effect" (up to 50% increase) and "significant effect" (50-200% increase). However, it should be noted that this applies to an initial stage before dilution of the leachable part of the residual products starts to occur. A reduction of the leachate content by a factor of 5-10 is obtained after only a few years. The environmental impact should not be evaluated solely on the basis of concentrations in leachate and thus in the affected ground water and/or surface water. The total amount in grammes, for example, is also of importance. Some data and comparisons are given in Table 3.
212
TABLE 3
Calculated quantities leachedfrom a I km stretch of road constructed of different materials, expressed in grammeslyear. The calculation is in respect of the initial stage of the leaching process (year 1). Metal Al Leachate from
Cd
Cr
cu
Ni
Pb
Zn
Graded slag (Malmo)
16-250
0.2-1.2
3-9
13-100
20-80
0.6-27
10-800
Graded slag (Linkoping)
7
<0.2
3
6
2
0.7
14
Natural gravel (Malmo)
800-3700 0.3-4
2-14
6-460
5-30
1-360
10-900
Natural gravel (LinkBping)
8
<0.2
2
14
0.1
0.1
19
Run-off water from test road (Malmo)
1-320
1-3
3-12
38-165
5-120
1-29
13-220
In all probability, the leaching properties of most fill materials in urban environments axe generally not more favourable than those of graded slag. In order to correspond to the background level in a natural environment (ground water), the leachate from such "graded slag" as has been studied here requires little dilution - in the order of a factor of 10. On the other hand, the amount of undiluted leachate necessary to achieve a significant effect on the environment corresponds to a factor 3-20 times higher than has been obtained in the leachate from "graded slag" and incinerator bottom ash. Calculation of leaching from natural gravel in Malmo (Table 3) is based, like the other annual amounts, on the data obtained for the test road in Malmo. It should be pointed out that this data only represents a short period of leaching and may be influenced by such factors as the infiltration of surface water and dust from various activities in the m a . In spite of the pronounced difference in leaching between natural gravel in Malmo and natural gravel in Linkoping, leaching must still be regarded as slight in all cases.
213
5.
PROCEDURES FOR UTILIZATION
The study and subsequent discussions with the Swedish EPA have shown that the utilization of screened bottom ash does not have a critical impact on the environment. The materiak should have the following properties: -
Rescreened ash through the separation of magnetic materials
- Maximum grain size 50 mm - No more than 10% of the particles smaller than 0.06 mm
-
The content of metals in leachates from the laboratory must not exceed those in the leachates
studied in the project - Loss on incineration less than 4% - The ash must be kept in storage for at least 3 months. The slag can be used chiefly for the following applications:
-
Embankment fill for roads Reinforcement material for low-traffic roads and bicycle paths - Fill under light buildings and floor structures
For the present, the guidelines below should normally be followed:
- The thickness of the fill should be limited to 3.0 m - The bottom ash should be placed primarily above the ground water - The bottom ash should be used primarily in urban areas and as fill.
level and below pavement
In an initial stage, general advice will be prepared for a small number of products, including sorted bottom ash from incineration and cementstabilized coal fly ash, for example. When sufficient experience has been gained over a few years, a general system ought to be drawn up and made available. The responsibility for this rests with the National Environment Protection AgeriCY.
The various suppliers ought to draw up procedures for the delivery of ash which include the following particulars: - quantity delivered - environmental quality assurance in respect of the delivered ash -
-
location
plan and section - control programme, if necessary
214
6.
ACKNOWLEDGEMENT
The authors wish to thank Sysav AB, who has given permission to publish data from the on-going project. We aslo want to thank Stiftelsen Reforsk, who is financing a major part of the studies.
7.
REFERENCES
Aubry, P,, Poncelet, E. & Billard, H. (1986).Mkheferes des usines d’aincineration d’ordures mtnageries: Charactdristiqueet utilisations - A.N.R.E.D. Service Recherches, Etudes et Dtvelopment. Hartlh, J. (1988). Incinerator ash utilkization in some countries in Europe. Roc. Ash IConference. Philadelphia. Hartlh, J. & Rogbeck, J. (1989). Sorted incinerator slag used as fill material. Roc. Int. Conf. on Municipal Waste Combustion, Vol. 1, p. 5B:1-13. ISBN 0-662 16891-7.
Jacobson, T. (1989). Provvag med sopfiirbrhningsrest i forsttirkningslager.Sysav, Malmii. National Road and Traffic Institute. VTI Notat V 104. Linkoping. Kullberg, S. (1990). Miljiiteknisk utvtirdering av provvagar vid an viindning av sopslagg och kolbottenaska i Malmo och LinkUping 1988-1990. Swedish Geotechnical Institute, Report No 2-482188. Lidcoping. Lundgren, T.& Hartlh, J. (1991). Slagganvandning - Teknik och miljo. Slutrapport. Stiftelsen Reforsk. Report (In print). Malmo.